Field of the Invention
The present invention relates to a thin-film piezoelectric material substrate, a thin-film piezoelectric material element having a piezoelectric material film and electrode film, a head gimbal assembly, an ink jet head having the thin-film piezoelectric material element, and method of manufacturing the thin-film piezoelectric material element.
Related Background Art
Piezoelectric material has been widely used for functional electronic components such as an actuator for generating deformation by applying voltage or a sensor for generating voltage from the deformation of elements in a reverse way, etc. A thin-film piezoelectric material, processed into thin-film like shape, is widely used for electronic device called MEMS (Micro Electro Mechanical Systems).
A lead (Pb)-based dielectric material having large piezoelectric characteristics, especially, Lead Zirconate Titanate, general formula, Pb(ZrxTi(1-x))O3-based perovskite-type ferroelectric called as “PZT”, has been widely used as conventional piezoelectric material.
Crystal structure of this piezoelectric material formed of PZT varies with the PbTiO3/PbZrO3 which is a ratio of Lead Titanate PbTiO3/Lead Zirconate PbZrO3. A morphotropic phase boundary (MPB) divides the ferroelectric phase region of PZT into two regions including a tetragonal phase region (FT) and a rhombohedra phase region (FR). As known, when the crystal structure is located at the morphotropic phase boundary (MPB), the free energy of the spontaneous polarization is quite high, thus PZT has the best electromechanical conversion property and the best piezoelectric property.
Further, PZT in the rhombohedra phase region has a large piezoelectric property when poling is along the c axis direction. Therefore, it is effective that crystal structure of the thin-film piezoelectric material made of PZT (referred to also as “PZT thin-film”) is oriented in a (001) direction.
When the thin-film piezoelectric material is applied to the MEMS, it is preferable that thin-film piezoelectric material layer made of high quality ferroelectric material (for example, PZT) is formed on a substrate having an insulating layer formed on its surface (referred to also as “insulator on Si substrate”). In this case, if oxide layer (SiO2) of the insulator on Si substrate is formed in a thin-film shape, the oxide layer can serve as a layer having some function, and also can serve as a stopping layer for Reactive Ion Etching. Therefore, it is ideal for MEMS to have thin-film piezoelectric material formed on the insulator on Si substrate, from point of views of the cost, manufacturing process and performance.
On the other hand, epitaxial growth is one of the most important method to control the crystal orientation of the PZT along the (001) direction. As conventional technology concerning formation of PZT thin-film on a Si single crystal substrate, for example, there is a technology disclosed in the U.S. Pat. No. 6,709,776 (referred also to as Patent Document 1). It is disclosed in the Patent Document 1 that buffer layer, metal thin-film, conductive oxide thin-film are formed sequentially on the Si single crystal substrate by epitaxial growth, and the PZT thin-film is formed on the oxide thin-film by epitaxial growth.
Further, it is disclosed in U.S. Patent Application Publication No. 2013/0093290 (referred also to as Patent Document 2) that seed layer made of Ti or TiO2 are formed on the insulating substrate, and PZT thin-film is deposited on the seed layer of epitaxial growth by the same step with the seed layer. It is disclosed in JP Patent Application Publication No. H6-350154 (referred also to as Patent Document 3) that a Ti layer is formed on the insulating substrate with sputtering and PZT thin-film is formed on the Ti layer with sputtering. The PZT thin-film is formed with (111) orientation.
It is conventionally known that PZT thin-film formed with sputtering has high heat-resistant therefore being able to improve flexibility in high-temperature processing (for example, Fujifilm research & development (No. 59-2014), referred also to as Non Patent Document 1).